Chris,
Looks like he's a little busy today.. He
pointed me to the shotimes forum to his old
posts...(his experiment was inconclusive as
he never did get to dyno the car, but maybe
the book can help point you in the right
direction)
Here's one...
As a little late night reading, I picked up a book called 'Design
Techniques for Engine Manifolds'. On page 183, they show an intake
manifold geometry not unlike the SHOs. They go through a long
description of how to make the engine perform better. How? You know
the cross-over that connects the front to back plenums that supports the
DIS. The suggestion is to close that passageway at low and high rpms,
and leave it open in the midrange for improved torque. The book has an
example that shows how this boosted low end torque and high end power by
10-15%. Not too shabby....so.....
Since I don't have access to a valve to slip into this passage way, I
did the next best thing. Yep, taped off the crossover so that the front
and rear plenums can not communicate (don't try this at home unless you
are brave). The results so far? Geez. It's hard to say...got to give
it a bit more time but my initial impression is that there is more
torque right around 3000-3200 rpm and less at 4000-5000 rpm.
Now the low/high rpm stuff, that is a bit more challenging to
characterize as it happens so quick or we so seldom drive at this rpm.
High rpm: I can't tell for sure..maybe a little more but I've already
got the LPM & 80 mm MAFS.
Low rpm: It doesn't have much pull, but I'm not sure I remember how much
pull my car had there.....it's not like we drive our SHOs at 2000 rpm
too often. I'll keep my car plugged for awhile longer and report back
if anything becomes more clear.
Sound: Hmmm...Something is definitely different here. I can't quite
put my finger on it, but the engine sounds quite a bit different. The
point of sealing this crossover is to make the intake manifold act like
two independent 3 cylinder engines...I don't ever remember envying the
sound of the Geo Metro coming out of the intake. You'll notice a
distinct and immediate difference before the secondaries open up in
terms of noise, after the secondaries open, it sounds just like your SHO
does today.
Just a thought for anyone who gets their SHO on a dyno with more than 1
run. To cap off the ends requires bolting the crossover back down (as
this is how the DIS is grounded) but this is still a 5 minute change
with a generous helping of duct tape (careful people, don't want to
scrape 3M off your pistons). This really needs analysis on a dyno.
The real story is that you probably won't be happy with just leaving the
cross-over plugged as it will drop torque somewhere in the middle, but
if the benefits are there as predicted, a valve that switches with rpm
in this crossover could boost low-end torque & power.
A downside? The SHO's long crossover length, makes this connection
between plenums a little less effective at boosting mid range torque so
the effect may not be as dramatic as predicted. With that said,
consider that the new Jaguar 3.0L engine utilizes at least 2 of these
communication valves between the plenums to perform some additional
tuning tricks.
While the Yamaha engineers who designed this engine might roll their
eyes at this mod, I'd bet not, certainly Ford might've been a little
concerned to allow them to add another valve in this passage to boost
power above that of the beloved Mustang GT back in '89. Just a thought
for the ever-experimenting.
BTW, Chris, I believe he does have the
patent around somewhere. If it gets into my
hands, I'll get it to you ASAP.
Quote from the big bro...
based on my posting another member found a series
of Yamaha patents on this and rekindled my interest. I have a copy of it.
It is from 1988 or 1989 I believe.
[This message has been edited by pornstar* (edited May 02, 2001).]
